My understanding is that master/slave more accurately describes the relationship than primary/replica does. A replica implies mirroring, but doesn't imply the other key components that differentiate it from the primary or master node.

I think leader/follower is just as accurate while carrying less baggage, but I could see people getting offended by those terms, too. Follower implies lack of autonomy, blind devotion as in a cult, a follower of a dictator like Hitler, power centered around a possible demagogue, etc.

If I were working on a new project I would probably not use "master/slave", because at that point it's trivial not to use it, but to ask an established project to change what they're doing for something so petty seems very silly.